Abstract: In one aspect of the invention, an OFDM receiver for receiving and demodulating OFDM signal comprises an automatic gain adjuster for adjusting the level of OFDM signal; a demodulator for demodulating a level-adjusted signal outputted from the automatic gain adjuster; a detector for detecting guard intervals contained in the OFDM signal; and a controller for controlling the automatic gain adjuster within the periods of guard intervals detected by the detector. In another aspect of the invention, an OFDM receiver includes a detector for detecting a level change of an OFDM signal and an automatic gain controller for adjusting the level of the OFDM signal in accordance with a signal level detected by the detector.

Abstract: A receiver has an oscillator for generating an oscillating signal at an oscillating frequency in accordance with an oscillation control signal, and receives a radio signal at a tuning frequency corresponding to the oscillating signal to demodulate the received radio signal. The receiver further includes a first frequency control loop system for generating a first control signal indicative of the difference in phase between a comparison signal generated by dividing the oscillating signal on the basis of the information on a channel selection frequency and a reference signal, and a second frequency control loop system for generating a second control signal indicative of a frequency difference between the oscillating frequency of the oscillating signal and the channel selection frequency. Either the first control signal or the second control signal is selectively supplied to the oscillator as an oscillation control signal.

Abstract: A receiver with an automatic receiving-station switching function for automatically switching a current receiving frequency from a reception frequency of a broadcast wave in reception to a reception frequency of a broadcast wave of another station, which is in a good reception condition, when a reception condition of the former broadcast wave becomes poor. After detecting deterioration of the reception condition of a received signal, when the level of a detected signal obtained by detecting the received signal is kept equal to or lower than a threshold value for a predetermined time or longer, the receiver sets muting means to a signal cutoff state to stop the audio output before the activation of the automatic receiving-station switching function. Even if the reception condition becomes poor, the muting means does not cut off an audio signal until the low level of the audio output in the currently receiving broadcasted program continues.

Abstract: An apparatus for acquiring tuning for a tuning frequency at a high speed. In a receiver, a tuning control unit holds inputted tuning frequency information at a designated address in accordance with a storage designation signal supplied from a control unit and controls the frequency of a VCO based on the tuning frequency information held at a designated address in accordance with a read designation signal supplied from the control unit. Further, in a frequency comparison loop including a frequency comparator for acquiring a frequency difference between a target tuning frequency and the VCO frequency, a count time setting circuit sets the count time for measuring the VCO frequency, and the count time is increased whenever measurement of the VCO frequency is repeated.

Abstract: A receiver has a plurality of receiving systems connected to a plurality of antennas, respectively, and a selective switching circuit for carrying out selective switching between output signals from the plurality of receiving systems to output an output signal from a receiving system in the most satisfactory receiving state, wherein the selective switching circuit has a fuzzy inference operation unit for discriminating receiving states of respective receiving states by a fuzzy inference. Accordingly, it is possible to synthetically judge the receiving state of the receiver to easily and stably select the optimum receiving system in the receiver.

Abstract: A noise reducing circuit for a receiver such as an FM receiver which is improved in noise reducing effect while reducing an unfamiliar feeling to and an erroneous operation of the receiver. The noise reducing circuit comprises fuzzy inference means for fuzzy inferring, using an input vector consisting of several factors defining a receiving input condition as a prerequisite, in accordance with fuzzy production rules provided by membership functions of the factors of the input vector, and a fuzzy controlling signal generating circuit for generating a fuzzy controlling signal for controlling a control object amount of any one of a separation control circuit, a frequency characteristic control circuit and muting circuit or each of any combination of the circuits in accordance with a result of inference produced by the fuzzy inference means.

Abstract: A radio receiver is disclosed having a wide filter and a narrow filter, each of which is connected with the front end and outputs an intermediate frequency signal. To the output of the filters are connected first and second detectors, respectively. A subtracter receives the outputs of the detectors and subtracts one from the other. A switch receives the output of the subtracter and directs the outputs of detectors in such a way that the switch is switched to a first position for directing the demodulated output from the first detector to a following circuit when the difference is below a reference level, and to a second position for directing the demodulated output from the second detector to the following circuit when the difference is above the reference level.

Abstract: A noise reducing circuit for reducing various noise in the output of a receiver. A noise attenuating circuit receives a demodulated signal and attenuates the noise in the demodulated signal in accordance with a control signal supplied thereto. A signal strength detecting circuit outputs a field intensity signal indicative of a strength of a radio wave signal inputted to the receiver. An output noise level detecting circuit outputs a noise level signal indicative of a noise level in the demodulated signal after the noise is attenuated. A fuzzy inferring circuit performs fuzzy inference in accordance with fuzzy production rules given by membership functions for the field intensity signal and the noise level signal, respectively so as to output an inference output. A control signal generating circuit produces the control signal on the basis of the inference output to control the noise attenuating circuit.

Abstract: A superheterodyne receiver in which unwanted lowering of the RF gain due to the presence of an interference signal outside the band of the desired signal is substantially eliminated. Levels of the outputs of both the RF amplifier and first mixer of the circuit are detected. The two level detection signals so produced are summed, and the sum signal applied to the gain control input terminal of the RF amplifier.

Abstract: A system and method for detecting the level of random noise contained in a band-limited amplitude-modulated signal. A sychronizing signal is produced which is .pi./2 out of phase with respect to the carrier of the amplitude-modulated signal. The amplitude-modulated signal and the synchronizing signal are multiplied together. Only a low frequency component is extracted from the multiplication output, and the low frequency component is taken as an indication of the level of the random noise contained in the amplitude-modulated signal.

Abstract: A synchronizing circuit used for both an AM intermediate frequency signal and an FM composite signal. A phase detector, voltage-controlled oscillator, frequency divider and phase shifter are connected in a phase-locked loop. The division factor of the frequency divider is controlled to different values for the AM and FM signals.

Abstract: An AM stereo demodulator with which the transition from the stereo receiving mode to the monaural receiving mode upon a reduction in the field strength of the received signal is made gradual so as to eliminate an abrupt change in the sound quality. For stereo demodulation, a pair of reference signals are generated which are .pi./2 different in phase for stereo reception. As the field strength of the received signal approaches the level where a phase-locked loop in the demodulator would become unlocked from the carrier of the received signal, the phase difference between the two reference signals is gradually reduced to .pi./4.

Abstract: A separation control circuit for a stereophonic receiver in which both the amount of separation between right- and left- channel signals is reduced and the amplification gain for higher frequency components of the two channel signals is reduced as the field strength of the received signal decreases. Thereby, the signal-to-noise ratio of the reproduced signal in the presence of a weak received signal is significantly improved. A single low-pass filter for each channel is used for both functions.

Abstract: An AM stereophonic receiver in which degradation of the quality of reproduced sound due to a decreased electric field strength is prevented. A main signal detector produces a sum signal representing the sum of first and second channel signals while a sub signal detector produces a difference signal representing the difference therebetween. The sum signal is coupled directly to a matrix circuit while the difference signal is coupled through a variable control type low-pass filter and a monophonic/stereophonic switch to the matrix circuit. The low-pass filter is controlled by a detection signal representative of the electric field strength of the received signal to reduce high frequency components when the electric field strength decreases below a predetermined value. The low-pass filter is bypassed when the electric field strength is sufficiently high.